DIY Direct X geothermal

[BrisbaneDIY]

I have modified my normal airconditioner's out door unit by disconnecting its Condensor and instead connecting a copper pipe buried loop in the ground. My system is 9kw system (3 HP). The ground loop (copper pipe) is about 96 metre (315 feet) in length burried at about 1.5 metre depth (5 feet depth) (summer average temperature at this depth is about 73 F ). The system is located at Brisbane, Australia. After charging up the system (R22), I am getting very high superheat (34 F), very low subcooling (5 F), Compressor head pressure and temperature is high (240 PSI and 183 F)and draws high current. Can any one comment on what is going on here.

[HVACRsaurus]

10 points for effort!

96 metres long seems like a lot. Imagine connecting a 100m long garden hose connected to a tap - probably only a trickle would come out..

Remember, condensers usually have multiple circuits for the purposes of reducing pressure drop, at the very least I reckon you've got dramas with pressure drop.

[Magoo]

single circuit of 1/2"copper pipe the pressure drop will be nominal 25 psig per 100 feet of pipe, add liquid condensing etc., will add more delta P. Perhaps a HX and use water and pump for ground heat sink condenser.

[BrisbaneDIY]

Hi Folks
I am positng the same question here with bit more info.


I have modified my normal R22 airconditioner's out door unit by disconnecting its Condenser and instead connecting a copper pipe buried in the ground. My system is 3 hp system. The ground loop (copper pipe) is about 315 feet in length buried at about 5 feet depth (summer average temperature at this depth is about 73 F. The system is at Brisbane. My problem is that the system has very high superheat (34 F), very low subcooling (5 F), Compressor head pressure and temperature are high (240 PSI and 183.2 F) and draws high current. Other related readings are,
Gas Line pressure = 68 PSI Temperature = 73.4 F
Liquid line pressure = 230 PSI Temperature = 105.8 F

Compressor Head pressure = 240 PSI Temperature = 183.2 F

Can any one comment on what is going on here.

[mad fridgie]

expansion device is to small.
head pressure is not high for a standard AC unit.

[Magoo]

hi mad,
You could be right, but at 68 psig R22 SST +4.0 'C and high suction temp at 23'C.
Standard a/c with remote condenser in effect. Something is out of balance. Brisbane, possibly + 35'C ambient though. Perhaps short of refrigerant, then dischage pressure would rocket if more gas was added to system, definite condenser pressure resistance.

[BrisbaneDIY]

Hi Magoo

The readings were taken when indoor temperature was 24.6 C (cool day for Brisbane summer). The temperature difference between return and discharge air indoors was about 8.6 C.

[mad fridgie]

hi mad,
You could be right, but at 68 psig R22 SST +4.0 'C and high suction temp at 23'C.
Standard a/c with remote condenser in effect. Something is out of balance. Brisbane, possibly + 35'C ambient though. Perhaps short of refrigerant, then dischage pressure would rocket if more gas was added to system, definite condenser pressure resistance.

High superheat, indoor coil is bing starved.
Liquid pressure is not really much lower than discharge pressure.
However liquid pressure may be to low for expansion device, thus reducing mass flow through the device.

[BradC]

When I put the big bphx in place of the condenser on my unit, I went from condensing at 60c to 25c. I had to replace the fixed orifice with an eev. I have a shallow water table, so I pump bore water through the hx and back into the ground. Glad to see another Aussie into geothermal.

[Tesla]

All above very good points. to fix dig it out and run same pipe with around 6 parallel circuits (in the ground) but the there will be more heat rejection and the ground media may not dissipate the heat so well. With a larger orifice the condenser will need to reject more heat and will require more area per volume of ground. My question is what is the ground media? dry dirt, wet dirt, sand or rocky stoney stuff? a little water in the ground media will make a big difference. Renew magazine has had a fair few examples of this system and calculations. for the Aussies and Kiwis degC is more understandable, along with psi for us older farts lol.

[BrisbaneDIY]

My question is what is the ground media? dry dirt, wet dirt, sand or rocky stoney stuff?

The ground is moist clay-ish type soil.

[Tesla]

So you know what to do now - bigger orifice and redo the ground coil. One last concern is can the compressor handle the jandle? So give it a go and no time like the present. Let us know how you go.

[Bigfreeze]

I have modified my normal airconditioner's out door unit by disconnecting its Condensor and instead connecting a copper pipe buried loop in the ground. My system is 9kw system (3 HP). The ground loop (copper pipe) is about 96 metre (315 feet) in length burried at about 1.5 metre depth (5 feet depth) (summer average temperature at this depth is about 73 F ). The system is located at Brisbane, Australia. After charging up the system (R22), I am getting very high superheat (34 F), very low subcooling (5 F), Compressor head pressure and temperature is high (240 PSI and 183 F)and draws high current. Can any one comment on what is going on here.

Your ground loop is far too small. If it were collecting heat you would need about 560m of loop ideally in 8 different loops and rejecting it is not too far of that either. You should'nt be collecting more than 15w per linear metre or rejecting more than 20w.